Further investigations in the assessment of Antarctic toothfish (Dissostichus mawsoni) in Subarea 88.2 SSRUs 88.2C–H for the years 2002–03 to 2012–13

Request Meeting Document

Document Number:

WG-SAM-14/29

Author(s):

S. Mormede, A. Dunn and S.M. Hanchet (New Zealand)

Submitted By:

Mr Doug Cooper (CCAMLR Secretariat)

Agenda Item(s)

WG-SAM-14 - 2.1 - A review of progress towards updated integrated assessments of toothfish

WG-SAM-14 - 2.2 - A review of stock assessment methodologies used in CCAMLR’s integrated toothfish assessments

Abstract

This paper presents further investigations of the Bayesian sex and age structured population stock assessment of Antarctic toothfish (Dissostichus mawsoni) in Subarea 88.2 covering SSRUs 88.2C, D, E, F, G, and H (SSRUs 88.2C–H). Annual age-length keys were applied, and the time trends in the tag-derived biomass index were investigated. The impact of hypothesised stock structure, fish movement, tag mixing and the potential for localised depletion on the stock assessment were also investigated.

We recommend the following:

That the Amundsen Sea region be considered as a single stock, with the stock assessment including all data from SSRUs 88.2C-H and the catch limit applied to the same region.
That R3 be chosen as the base case model for providing management advice for the 2014/15 fishing year once it has been updated with the 2014 fishery data.
That ways to obtain a better estimate of the biomass in SSRUs 88.2C-G are considered, in particular by improving the spatial overlap between tags released and subsequent fishing effort.
That the recent high exploitation rates and localised depletion in SSRU 88.2H is recognised by allocating a greater proportion of the catch limit to SSRUs 88.2C–G and less to SSRU 88.2H.
That all Members, where possible, contribute to the development of annual age-length keys, using approved otolith reading protocols and aging validation.